Hydraulic transfer is known in which a transfer film including a water-soluble film (carrier sheet) and an appropriate water-insoluble transfer pattern formed thereon in advance is placed on a transfer liquid (typically, water) in a transfer liquid tank to wet the transfer film (water-soluble film) with the transfer liquid, and a work piece is brought into contact with the transfer film and forced into the liquid in the transfer liquid tank to transfer the transfer pattern on the transfer film to the surface of the work piece by the action of the hydraulic pressure. The transfer film includes a water-soluble film and a transfer pattern of an ink formed (printed) thereon in advance as described above, and the ink of the transfer pattern is dry. Thus, in performing the transfer, a solvent or non-solvent activator needs to be applied to the transfer pattern on the transfer film to restore the transfer pattern into the same wet state as the transfer pattern immediately after printing, that is, a state where the transfer pattern has adhesion. This processing is called activation.
A known activation process is an activator applying process that involves using a spreading roller, such as a gravure roll coater or a kiss-touch roll coater. This process is to activate the ink before the transfer film is introduced (fed) into the transfer liquid tank.
Some hydraulic transfer techniques have been disclosed in which an additive pigment, such as a color pigment, is contained not only in the transfer pattern on the water-soluble film but also in the activator that dissolves the transfer ink, and the applicant has filed several patents for such techniques (see Patent Literatures 1 to 3, for example).
With such techniques, the additive pigment is disposed on the transfer ink of the transfer pattern (between the work piece and the transfer ink after transfer), while the shape of the transfer pattern is substantially unchanged, even though the transfer ink of the transfer pattern on the water-soluble film bulges out (expands) on the liquid surface because of the additive pigment contained in the activator. Thus, a wider variety of design elements (variations of color of the transfer pattern) can be imparted to the same transfer pattern.
An important advantage of this is that a wide variety of design elements can be provided by the color of the work piece itself or the color of the additive pigment in the activator without changing the transfer pattern on the water-soluble film (that is, without increasing the number of gravure printing plates).
However, the conventional techniques, that is, the techniques of imparting a wide variety of design elements by using the additive pigment contained in the activator can be used only when the additive pigment is uniformly added over the entire surface of the transfer pattern on the water-soluble film. In addition, those techniques have a problem that a difference or variation in color, grain size and blending of the additive pigment has a great effect on the desired design element (such an effect on the design element is referred to as a “streak”, which will be described later) and therefore it is extremely difficult to handle the activator blended with the additive pigment.
In particular, if the additive pigment has a specific gravity different from that of a liquid constituent of the activator, it is necessary to maintain dispersion of the additive pigment in the activator from the viewpoint of design reproducibility. Even if dispersion of the additive pigment in the activator can be maintained, if a phenomenon called a streak occurs during application of the activator, a problem arises in that the streak has an effect on the design of the resulting article with a hydraulically transferred pattern, and the problem needs to be solved. This problem is marked if the additive pigment is a lustrous pigment that has a high luster.
More specifically, when the inventor performs hydraulic transfer using an activator containing a lustrous pigment having a high luster (a pigment containing many fine scale-shaped pieces of a metal) as an additive pigment, there arise problems in that the article with a hydraulically transferred pattern has a design element that provides unstable intense reflected light and that a pattern called a “streak” is accidentally formed.
In particular, in a mass production phase, the larger the scales of lustrous pigment is, or the greater the difference in specific gravity the pigment has, the more significantly the pigment settles down or the concentration of the pigment varies before activation, and the more marked the uncontrollable change in color design is.
Next, the “streak” will be described. The “streak” is a visible line of the additive pigment formed on the transfer film as a result of uneven dispersion of the additive pigment at a site where the content or concentration of the additive pigment in the activator adhering to the spreading roller significantly varies. The “streak” is a phenomenon that occurs irregularly and therefore has generally been handled as a defective design element.
A cause of occurrence of the “streak” is contact of the surface of the spreading roller with a liquid, for example. The occurrence probably involves various factors, such as the site of unevenness of the flow of the activator, the position of a bubble dwelling on the liquid surface or a bubble adhering to a part of the surface of the spreading roller, or the position where the excessive activator scrapped off by a doctor knife drops along the spreading roller.